The present invention relates to a printing control device for a thermal printer used with an electronic portable calculator.
A thermal printer has a slidable printing head having a number of printing elements. The printing head slides on a sheet of heat-sensitive paper to print characters or the like on it. To use such a thermal printer with an electronic portable calculator, the printing head must be supplied with a low voltage thereby to reduce power consumption.
When the voltage applied to the printing head is lowered due to use of a cell of small capacity, in printing a letter "H", for example, the "I" parts will be printed less distinct than the "-" part. This is because more printing elements must be heated to print either "I" part than to print the "-" part. That is, the more printing elements that are heated at the same time, the lower is the voltage that is applied to each of them. This unwanted phenomenon is promoted because a considerable voltage drop occurs due to resistances in a common line connecting the printing elements to the cell when the voltage is applied to the printing head.
When the voltage applied to each printing element is the lowest possible, however, the printing elements are not sufficiently heated when the printing head begins printing characters or the like on the first line. Inevitably a first few characters or the like will be insufficiently distinct unlike the others on the first line. As a result, due to their different distinctnesses, the characters or the like appear unattractive.